Two Problems with Distributed Systems: Data Access Control and Memory Shering

! Distributed computer system is a set of autonomous computers connected by a network of transmission channels and equipped with a distributed system software. This is a work environment for a class of tasks of common objective; the network is a communication infrastructure only. Main features of distributed systems dealt with here are: • absence of common clock for all computers – no global time provided by external service • absence of physical memory common to each computer-message exchange by the network A schematic structure of distributed system with distributed shared memory (DSM) is illustrated in Fig. 1 ([Cz 2012]). Assumptions and denotations: • the computers work in parallel and are numbered 1,2,...,n • reading and writing is governed by the memory manager of each computer;